Overall and demographic subgroup incidences of alopecia areata, alopecia totalis, and alopecia universalis in the United States
Authors: Inkyu E. Kang, Andrew Strunk, Amit Garg
Journal: Journal of the American Academy of Dermatology (2023)

Previous studies on alopecia areata (AA) incidence in the United States and abroad are limited by unrepresentative samples and lack of subgroup analysis, which reduces generalizability.1Safavi K.H. Muller S.A. Suman V.J. Moshell A.N. Melton III, L.J. Incidence of alopecia areata in Olmsted County, Minnesota, 1975 through 1989.Mayo Clin Proc. 1995; 70: 628-633Abstract Full Text Full Text PDF PubMed Scopus (474) Google Scholar, 2McKenzie P.L. Maltenfort M. Bruckner A.L. et al.Evaluation of the prevalence and incidence of pediatric alopecia areata using electronic health record data.JAMA Dermatol. 2022; 158: 547-551Crossref PubMed Scopus (10) Google Scholar, 3Ali N.S. Tollefson M.M. Lohse C.M. Torgerson R.R. Incidence and comorbidities of pediatric alopecia areata: a retrospective matched cohort study using the Rochester Epidemiology Project.J Am Acad Dermatol. 2022; 87: 427-429Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar, 4Soh B.W. Kim S.M. Kim Y.C. Choi G.S. Choi J.W. Increasing prevalence of alopecia areata in South Korea.J Dermatol. 2019; 46: e331-e332Crossref PubMed Scopus (10) Google Scholar To estimate overall and subgroup incidences of AA, alopecia totalis (AT), and alopecia universalis (AU) in the United States, we performed a retrospective study of the Explorys database. The study population comprised patients with at least one encounter between April 1, 2016, and December 31, 2019, within a 15% random sample of the database population. The use of a 15% random sample is based on our institution's access agreement with the data proprietor (IBM). One year of observable person-time was required before the start of follow-up to ensure adequate time for identification and exclusion of prevalent cases. For each patient, follow-up began on the latest of April 1, 2016 or the day following the 1-year baseline period. Patients with missing sex or age (0.75% total) were excluded. Cases of AA were identified by at least one of the International Classification of Diseases codes (704.01 or L63.x) occurring during follow-up. Cases of AT and AU were identified by at least one record of codes L63.0 and L63.1, respectively. These case definitions have positive predictive values of 89% for AA, 64% for AT, and 86% for AU.5Lavian J. Li S.J. Lee E.Y. et al.Validation of case identification for alopecia areata using international classification of diseases coding.Int J Trichology. 2020; 12: 234-237Crossref PubMed Google Scholar Incidence rates (IRs) were adjusted for age and sex using direct standardization to facilitate group comparisons. Among 3,057,186 eligible patients, the standardized IR of any AA was 21.1 (95% CI, 19.8-22.3) per 100,000 person-years (PYs). Crude and standardized IRs according to age, sex, and patient-reported race/ethnicity are presented in Table I. Relative to White, standardized incidence rate ratios (IRRs) for Asians, Hispanics/Latinos, and Blacks were 3.02 (95% CI, 2.59-3.52), 1.46 (95% CI, 1.17-1.81), and 1.30 (95% CI, 1.19-1.41), respectively. Among 1128 newly diagnosed patients in whom subtype could be specified by the International Classification of Diseases-10 codes, 69 (6.1%) and 33 patients (2.9%) were diagnosed with AT and AU, respectively.Table IOverall and subgroup incidences of alopecia areata, including all subtypesGroupAlopecia areata cases, all subtypesTotal # of patientsTotal follow-up time (PY)Crude incidence rate per 100,000 PY (95% CI)Standardized∗Overall incidence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific incidences are standardized by age. Age-specific incidences are standardized by sex. Race-specific incidences are standardized by age. incidence rate per 100,000 PY (95% CI)Overall12003,057,1865,919,23020.3 (19.1-21.5)21.1 (19.8-22.3)SexFemale7651,727,4993,365,53622.7 (21.1-24.4)23.0 (21.4-24.7)Male4351,329,6872,553,69417.0 (15.5-18.7)18.8 (17.0-20.7)Age group (y)Pediatric (0-17)278669,2271,328,03420.9 (18.5-23.5)20.9 (18.5-23.5)0-9156386,697748,04420.9 (17.7-24.4)21.1 (17.9-24.6)10-17122282,530579,98921.0 (17.5-25.1)21.0 (17.5-25.1)Adult (18+)9222,387,9594,591,19620.1 (18.8-21.4)19.4 (18.2-20.8)18-29188418,028770,50624.4 (21.0-28.1)25.1 (21.5-29.0)30-39214352,238654,90832.7 (28.4-37.4)32.9 (28.5-37.7)40-49158353,892681,98723.2 (19.7-27.1)22.7 (19.2-26.6)50-59161430,298852,87418.9 (16.1-22.0)17.8 (15.1-20.8)60-69127408,667823,10015.4 (12.9-18.4)14.6 (12.1-17.4)70-7957259,821516,20511.0 (8.4-14.3)10.4 (7.9-13.5)80-8917165,015291,6175.8 (3.4-9.3)5.3 (3.0-8.5)Race†Overall, 520,615 patients were missing race. Patients missing race were included in the estimates of AA incidence for the overall group, and sex/age subgroups.White6601,961,8233,764,46117.5 (16.2-18.9)18.6 (17.2-20.1)Black163329,691700,78423.3 (19.8-27.1)24.1 (20.5-28.2)Asian3933,86566,49858.6 (41.7-80.2)56.2 (39.5-77.5)Hispanic/Latino1938,39865,06329.2 (17.6-45.6)27.1 (16.3-42.4)Other/Multiracial122172,794308,56239.5 (32.8-47.2)39.7 (33.0-47.5)PY, Person-year.∗ Overall incidence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific incidences are standardized by age. Age-specific incidences are standardized by sex. Race-specific incidences are standardized by age.† Overall, 520,615 patients were missing race. Patients missing race were included in the estimates of AA incidence for the overall group, and sex/age subgroups. Open table in a new tab PY, Person-year. Overall IR of AT was 1.1 (95% CI, 0.8-1.3) per 100,000 PY after age- and sex-adjustment. IRRs for AT were 1.14 (95% CI, 0.62-2.09) for adults aged ≥18 years relative to pediatric patients and 2.55 (95% CI, 1.44-4.51) for women relative to men. Age- and sex-adjusted IR of AU was 0.5 (95% CI, 0.4-0.8) per 100,000 PY. Age-standardized IRR of AU for women compared with men was 1.46 (95% CI, 0.70-3.06) (Table II).Table IIOverall and subgroup incidences of alopecia totalis and alopecia universalis∗Incidence estimates for AA subtypes in race/ethnic subgroups were not reported due to low number of events and corresponding imprecision.GroupCasesTotal # of patientsTotal follow-up time (PY)Crude incidence rate per 100,000 PY (95% CI)†CIs for crude and standardized incidence rates were based on the Poisson and gamma distributions, respectively.Standardized‡Overall incidence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific incidences are standardized by age. Age-specific incidences are standardized by sex. incidence rate per 100,000 PY (95% CI)†CIs for crude and standardized incidence rates were based on the Poisson and gamma distributions, respectively.Alopecia totalisOverall693,057,1865,920,7941.2 (0.9-1.5)1.1 (0.8-1.3)SexFemale531,727,4993,366,5611.6 (1.2-2.1)1.5 (1.1-1.9)Male161,329,6872,554,2330.6 (0.4-1.0)0.6 (0.3-1.0)Age group (ye)Pediatric (0-17)13669,2271,328,4081.0 (0.5-1.7)1.0 (0.5-1.7)Adult (18+)562,387,9594,592,3861.2 (0.9-1.6)1.1 (0.8-1.4)18-4415936,7881,742,7370.9 (0.5-1.4)0.8 (0.4-1.3)45-6423830,6491,647,1851.4 (0.9-2.1)1.3 (0.8-1.9)65+18620,5221,202,4651.5 (0.9-2.4)1.4 (0.8-2.2)Alopecia universalisOverall333,057,1865,920,8400.6 (0.4-0.8)0.5 (0.4-0.8)SexFemale221,727,4993,366,5980.7 (0.4-1.0)0.6 (0.4-1.0)Male111,329,6872,554,2420.4 (0.2-0.8)0.4 (0.2-0.8)Age group (years)Pediatric (0-17)9669,2271,328,4110.7 (0.3-1.3)0.7 (0.3-1.3)Adult (18+)242,387,9594,592,4290.5 (0.3-0.8)0.5 (0.3-0.7)18-449936,7881,742,7400.5 (0.2-1.0)0.5 (0.2-1.0)45-6411830,6491,647,2010.7 (0.3-1.2)0.6 (0.3-1.1)65+4620,5221,202,4880.3 (0.1-0.9)0.3 (0.1-0.8)AA, Alopecia areata; PY, person-year.∗ Incidence estimates for AA subtypes in race/ethnic subgroups were not reported due to low number of events and corresponding imprecision.† CIs for crude and standardized incidence rates were based on the Poisson and gamma distributions, respectively.‡ Overall incidence is standardized by age and sex using the direct method and population estimates from the 2019 US Community Survey. Sex-specific incidences are standardized by age. Age-specific incidences are standardized by sex. Open table in a new tab AA, Alopecia areata; PY, person-year. We observed a significant burden of newly diagnosed AA in the United States, in which people of color, particularly Asian Americans, appear to be disproportionately affected. Incidence of AA was also greater among Black and Hispanic/Latino than Caucasians. AT and AU incidence were similar for adults aged ≥18 years and pediatric patients. Patients with mild AA may have been overlooked in this study because of lower likelihood of seeking care, leading to underestimation of incidence. Validity of AA diagnosis codes applied by nondermatologists is unknown. Strengths of this analysis include large sample size, cohort diversity, and standardization of AA incidence estimates using 18 age- and sex-specific strata, all of which support generalizability. Dr. Garg is an advisor for AbbVie, Aclaris Therapeutics, Anaptys Bio, Aristea Therapeutics, Boehringer Ingelheim, Bristol Myers Squibb, Incyte, Insmed, Janssen, Novartis, Pfizer, Sonoma Biotherapeutics, UCB, Union Therapeutics, Ventyx Biosciences, and Viela Biosciences, and receives honoraria. Dr Garg receives research grants from AbbVie, UCB, National Psoriasis Foundation, and CHORD COUSIN Collaboration (C3). He is co-copyright holder of the HS-IGA and HiSQOL instruments. The other authors declare no conflicts of interest.